Electric cable



April 16, 1946. w. T. PEIRCE 2,398,447

ELECTRIC CABLE Filed Oct. 26, 1943 INVENTOR IIQILTER ZPE/RCE,

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Patented Apr. 16, 1946 ELECTRIC CABLE Walter T. Peirce, Worcester, Mass, assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey Application October 26, 1943, Serial No. 507,693

14 Claims.

This invention relates to an electric cable and .more particularly to cables having oil or oil saturated insulation of the type shown in the Thompson Patent No. 2,138,362, and in the Peterson Patent No. 2,316,808.

In this type of cable, the electrical conductors and insulation are enclosed in an oiltight sheath. Due to temperature changes the pressure within the cable will vary if compensating means are not provided. This causes trouble due to ionization and also distortion and breakage of the sheath. Various compensating means have been proposed as shown in the above mentioned patents.

It has been proposed to use capillary tubes but they have certain limitations. It has been found that it is difficult to effect stabilization over long lengths of cable such as one or more miles in length through tubes of capillary size. A single capillary tube cannot contain a large amount of oil and therefore it is necessary to use a plurality of such tubes in order to take care of large temperature or pressure changes.

With the cables now in use there is the possibility that the pressure within the cable will fall below atmospheric. This condition is undesirable and it is an object of this invention to provide an electric cable in which the pressure of the oil will always be above atmospheric.

Another object is to provide a capillary tube having a relatively large crosssectional area.

A still further object is to provide an electric cable having means for keeping the pressure throughout the length of the cable constant.

These and other objects will be more apparent after referring to the following specification and attached drawing, in which:

Figure 1 is a cross-sectional view of the cable;

Figure 2 is a side View of the cable shown in Figure 1 with certain parts of the cable removed to more clearly disclose its structure; and

centric tubes I2 and I4 is filled with fibrous material Hi.

In the manufacture of the cables the conductors 2 and the concentric tubes l2 and I are twisted together in spiral form. The lay of this spiral, that is, the distance between the bottom loops 18, in ordinary cable is between 40 to 80 inches. These cables are ordinarily made in lengths of 200 to 500 feet and these lengths are joined as shown at 20 in Figure 3. The outer concentric tube I2 is perforated at short intervals, preferably at 1 times the length of the lay of the cable so that perforations would occur every 50 to 90 inches in the tube. As shown, three concentric tubes are usedand in this case the perforations in any one tube may be at three times this distance with the openings occurring in the tubes successively so that there will be an opening every 50 or 90 inches throughout thelength of the cable.

The concentric tubes I2 and H are filled with an inert gas such as nitrogen or helium. As the oil expands, due to the rising temperature of the cable, the resulting pressure forces the oil into the openings 22 in the cable-where it collects at the low spots l8 between the tubes. The tubes l2 and M are so spaced that the oil is retained therein due to capillary action. By using con- 7 centric tubes, a large increase in the surface area Figure 3 is a schematic sketch showing the op- I eration of the system within the cable.

Referring more particularly to the drawing, the reference numeral 2 indicates the metallic conductors of the cable, each of which is surrounded by oil impregnated insulation 4. A metallic tape 6 surrounds the insulation 4 and a metallic and fibrous binder 8 holds the three conductors 2 together and makes contact between the metallic tape 6 and the impervious sheath III which surrounds the entire cable. Between the conductors 2 are a plurality of concentric tubes 12 and [4. The space in the interstices between the conductors not occupied by the conin contact with the oil is provided, thus causing the oil to have a greater tendency to form capi1- lary blocks with a larger bore. This provides the space required to take care of the oil and gas expansion and contraction. The trapped oil in the low spots l8 blocks off the gas which is normally in the tube and causes the gas to collect in separate segments at the top of the loops 24. As the oil rises in the space between the concentric tubes, the gas is put under pressure and as the cable cools off the pressure of the gas drives the oil back into the cable through the openings 22 and thus the system operates with a very narrow pressure swing.

It is desirable to stabilize the pressure of the system at some positive value so that in none of the pressure swings would the pressure within the cable go below atmospheric. This is accomplished as follows:

At one of the joints 20 an oil or a gas reservoir 26 is provided. Within this reservoir is a supply of oil 28 which is fed to the cable by means of tube 30. The oil entering the joint 20 through the tube 30 will replace the oil that flows from the cable through the openings 22 into the oil trap l8. The top portion 32 of the reservoir 26 is filled with the inert gas and a stand pipe 34 is con-' 1 fective over long lengths of cable by means of the pressure transmitting qualities of the tubes them- I selves.

The collecting of the oil in the low sections it of the tubes interferes with the transmission of the pressure from the reservoir 28 to distant parts of the cable due to the friction of the oil against the walls of. the capillary tubes l2 and M. It is impossible to transmit this pressure over dis tances greater than 200 or 300 feet and even in a such distances there a gradual diminution in ing claims.

I claim:

1. A cable comprising a conductor, insulation about the conductor including an oil, a fluidtight sheath about the insulation, a tube between the conductor and sheath, a second tube containing as surrounding and substantially parallel to said first tube, said outer tube having an opening therein for admitting oil thereto, the space between said tubes beingsuch that the oil is retained therein due to capillary action.

2. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a helical tube between the conductor and sheath, a second tube containing gas surrounding and substantially parallel to said first tube, said tubes providing a dome containing trapped gas, said outer tube having an opening therein for admitting oil thereto to provide contact between the trapped gas and the oil, said opening being so positioned that thetrapped gas is retained in the dome by the oil.

3. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a tube between the conductor and sheath containing gas, a second tube containing gas surrounding and substantially parallel to said first tube, said outer tube having openings therein for admitting 011 thereto, the space between said tubes being such that the oil is retained therein due to capillary action, said inner tube having an opening therein to transfer the pressure of said gas past the oil between said tubes.

4. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a tube between the conductor and sheath containing as, a tube containing gas surrounding and substantially parallel to said first tube, said tubes providing a dome containing trapped gas, said outer tube having an opening therein for admitting oil thereto to provide contact between the trapped gas and the aeea-iu 011, said. opening being so positioned that the trapped gas is retained in the dome by the oil, said inner tube having an opening therein at said dome to transfer the pressure or said gas past the oil between said tubes.

5. A cable comprising a conductor, insulation about the conductor including an oil, a fluidtight sheath about the insulation, 2. tube between the conductor and sheath containing gas, a second tube containing gas surrounding and substantlally parallel to said first tube, said outer tube having openings therein for admitting oil thereto, the space between said tubes being such that the oil is retained therein due to capillary action, said inner. tube having an opening therein to transfer the pressure of said gas past the oil between said tubes, and a reservoir containing gas under pressure connected to said tubes.

A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath. about the insulation, a tube between the conductor and sheath containing gas, a second tube containing gas surrounding and substantially parallel to said first tube, said outer tube having openings therein for admitting oil thereto, space between said tubes being such that the oil is retained therein, due to capillary action, said inner tube having an opening therein to transfer the pressure of said gas past the oil between said tubes, and a reservoir containing gas under pressure connected to said tubes, said reservoir also containing oil connected to the oil in said cable,

I. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a tube between the conductor and sheath containing gas, a tube containing gas surrounding and substantially parallel to said first tube, said tubes providing a dome containing trapped gas, said outer tube having an opening therein for admitting oil thereto to provide contact between the trapped gas and the oil, said opening being so positioned that the trapped gas is retained in the dome by the oil, said inner tube having an opening therein at said dome to transfer the pressure of said gas past the oil between said tubes, and a reservoir containing gas under pressure connected to said tubes.

8. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight; sheath about the insulation, a tube between the conductor and sheath containing gas, a tube contaming gas surrounding and substantially parollel to said first tube, said tubes providing a dome containing trapped gas, said outer tube having an opening therein for admitting oil thereto to provide contact between the trapped gas and the oil, said opening being so positioned that the trapped gas is retained in the dome by the oil, said inner tube having an opening therein at said dome to transfer the pressure of said gas past the oil between said tubes, and a reservoir containing gas under pressure connected to said tubes, said reser- Von" also containing oil connected to the oil in said cable.

9. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a tube between the conductor and sheath containing gas, a tube containing gas surrounding and substantially parallel to said first tube, said tubes providing domes containing trapped gas, said outer tube having an opening between the domes for admitting oil thereto to provide contact between the trapped aseaqm gas and the oil, said openings being so positioned that the trapped gas is retained in the domes by the oil, said inner tube having an opening therein at one of said domes to transfer the pressure of said gas past the oil between said tubes.

10. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a tube between the conductor and sheath containing gas, a tube containing gas surrounding and substantially parallel to said first tube, said tubes providing domes containin trapped gas, said outer tube having an opening between the domes for admitting oil thereto to provide contact between the trapped gas and the oil, said openings being so positioned that the trapped gas is retained in the domes by the oil, said inner tube having an opening therein at one of said domes to transfer the pressure oi said gas past the oil between said tubes, and a reservoir containing gas under pressure connected to said tubes.

11. A cable comprising a conductor, insulation about the conductor including an oil, a fluid-tight sheath about the insulation, a tube between the conductor and sheath containing gas, a tube containing gas surrounding and substantially parellel to said first tube, said tubes providing domes con- 12. A cablev comprising a conductor, insulation about the conductor including a liquid, a fluidtight sheath about the insulation, a tube crmtaining gas disposed within said sheath, said tube having a part thereof elevated above the remainder of said tube, an outer tube originally containing gas surrounding and substantially parallel to the first tube and providing a space therebetween, said outer tube having openings at intervals to provide access between the liquid and the space between tubes, said first mentioned tube having openings at much longer intervals than the outer tube to provide access between the gas in the first tube and the space between tubes.

13. A system of electrical transmission consisting of a plurality of lengths of cable and joints.

between said lengths, said cable comprising a conductor, insulation about the conductor including a liquid, a fluid-tight sheath about the insulation, a tube containing gas disposed within said sheath, said tube having a part thereof elevated above the remainder of said tube, an outer tube originally containing gas surrounding and substantially parallel to the first tube and providing-a space therebetween, said outer tube having openings at intervals to provide access between the liquid and the space between tubes, said first mentioned tube having openings at said joints to provide access between the gas in the first tube and the space between tubes. and a reservoir external to said cable containing gas connected to said first mentioned tube.

14. A cable comprising a conductor, insulation about the conductor including a liquid, a fluidtight sheath about the insulation, a tube containing gas disposed within said sheath, and an outer tube originally containing gas surrounding and substantially parallel to the first tube and pro viding a space therebetween, said outer tube having an opening therein for admitting liquid thereto.

WALTER T. PEIRCE. 

